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        /* 
             九九乘法表:双重for循环

             *
             **
             ***
             ****

             i    num(j 的最大值)
             0     1
             1     2
             2     3
             
             i + 1 = num
        */
        for (let i = 1; i < 10; i++) {

            let star = '';
            for (let k = 1; k < i + 1; k++) {
                star = star + (i + "*" + k + "=" + i * k) + " ";
            }
            console.log(star);
        }

        // 代码是调试出来，不是写出来的。
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